I'm not terribly familiar with the horror genre, so I don't feel like the best judge of this as a work of horror in terms of tropes, but I liked how the themes of loss/grief and responsibility were continuous through the story.  There are some reviews that I saw that said the ending feels like a deus ex machina and really out of nowhere, and while that makes sense if you are judging this as a zombie story, I personally feel like it was consistent with the themes I previously mentioned.